The magnitude 6.7 quake struck in the Pacific Ocean, some 202 miles southeast of the capital, at 7.49am local time (23.49pm BST on Wednesday), according to the US Geological Survey.

The epicentre was off the coast of Hachijo, a small island to the east of the mainland, Sky News reports.

Japan 's Ministry of Energy, Trade and Industry says that there were no reports of damages to the country's power plants.

While Tuesday morning's quake caused speculative buying among small construction stocks, Thursday's quake is unlikely to trigger any major share movements, an analyst at one Japanese brokerage said, The Wall Street Journal reports.

Meanwhile, the quake was only "a rehearsal for us in preparing for a bigger, real disaster", said one resident, fisheries official Masaki Yamada, in the port of Yaizu near the offshore epicentre.

The experts agree. The Earthquake Research Committee warns of an 87 percent chance that a magnitude-eight earthquake -- 100 times more powerful than this week's tremor -- will strike the same region within the next 30 years.

For the neighbouring Kanto plains, home to Tokyo's vast urban sprawl, the chance of a major quake of magnitude seven for the same period is 70 percent, said the government agency, which revises the probabilities every year, AFP reports.

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